The UCLA/Caltech Program in Engineered Immunity is conducting a series of adoptive cell therapy clinical investigations using F5 MART T cell receptor (TCR) engineered T cells. T lymphocytes engineered to express this high affinity TCR are highly cytotoxic towards HLA A*0201/ MART-positive melanoma targets, release type I cytokines and are biologically very active when administered to patients. In a recently completed trial in which 109 F5 MART CTL were administered to 8 conditioned patients with metastatic melanoma, 6 showed evidence of dramatic tumor regression in measurable disease sites such as lung, liver, bone, lymph node and skin. All however, relapsed within three months. Our objective is to study the mechanism of sensitivity or resistance of early passage patient-derived melanoma cell lines from these patients, and from two successor trials, to F5 MART CTL-induced cytotoxicity. We hypothesize that epigenetically controlled deregulated activation of signaling pathways and an imbalance in the ratio of pro- and anti-apoptotic gene products favor an immune-resistant phenotype. Further, the acquired and/or inherent resistance can be reversed by chromatin remodeling molecules such as HDACi (SAHA). Successful execution of the proposed specific aims will identify epigenetically regulated signal transduction pathway(s) and apoptosis-associated gene products responsible for melanoma resistance to F5 MART CTL. This culminates in the utilization of small molecule inhibitors (sensitizing agents) that can specifically target the components of deregulated signaling pathways and by modulating the expression profile of apoptosis-related gene products favor a pro-apoptotic milieu, thus, conferring a sensitive phenotype.